In the past, a number of different problems have frustrated the utilization of polyurethane foam as a medical cast material despite the clear advantages of such a composition for that purpose. One particularly vexing problem has centered on the difficulty of physically applying the comparatively fragile, uncured foam to the injured limb which is to be immobilized. Spraying of the foam directly onto the limb has presented obvious containment difficulties; and injection of incipiently curing foam into a tubular sleeve has resulted in a finished cast lacking the necessary uniformity of its physical properties.